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158                PRACTICAL ORGANIC CHEMISTRY
nitrite, dissolved in a small quantity of water, is then slowly
added with frequent stirring. The separation of the hyclro-
chloride of nitrosodimethylaniline in the form of small yellow
needles soon begins, and the liquid is gradually filled with, a
thick crystalline deposit. When, after standing for a short time
(half an hour), no further increase in the quantity of crystals is
observed, the mass is filtered at the pump and washed with
spirit, to which one or two c.c. of concentrated hydrochloric
acid has been added. It is then washed once or twice with
spirit, drained and pressed on a porous plate. Yield, nearly
theoretical. It may be recrystallised by adding small quantities
of hot water, until the salt is just dissolved, and then setting'
aside to cool. If the free base is to be prepared, recrystallisa-
tion is unnecessary. Ten grams of the hydrochloride are-mixed
into a paste with water in a flask, and caustic soda solution added
in the cold until alkaline. The yellow colour of the salt changes
to green of the free base. Sufficient ether is added to dissolve
the green precipitate. The ethereal solution is carefully
separated by means of a separating-funnel and most of the ethei'
is then removed by distillation. The remaining liquid is poured
out into a beaker and set aside to crystallise. The base remains
on evaporation of the ether in the form of brilliant green foliated
crystals.
CGH5N(CH3)2HC1+HNO2-(NO)C0H4N(CH3).,HC14-H1JO
Properties.—Large green foliated crystals ; m. p. 85".
Reactions.-—i. Dissolve a few crystals in dilute hydrochloric
acid and add a little zinc dust. The solution is decolourised
through the formation of dimethyl ^-phenylenediarnine,
(CH3)aN.C8H4NH2.
2.   Warm a few of the crystals with yellow ammonium sul pli i de
solution for a few minutes, acidify with hydrochloric acid,   and
finally add a little ferric chloride.     A deep blue colouration- is
produced, due to the formation of methylene blue.
3.   Dissolve 6 grams of caustic soda in 250 c.c. of wa'ter   mid
heat to boiling.     Add 5.grams of the hydrochloride of nitroso-
dimethylaniline gradually.    The free base, which separates out in
oily drops, is allowed to dissolve before each fresh addition*      The
boiling is continued until the dark green colour of the liquid